This is a regression in JavaFX 1.2 build 8 (it was working in build 6).

If you create a ProgressBar control and set the progress variable to an expression that evaluations to NaN, the control will block all UI input for the entire window. Usually you would not set the progress value to NaN intentionally, but this is a common initial state for complex bound calculations. Also, this defect is rather hard to debug, because it prevents all user interaction with the application and gives no indication that the ProgressBar is the culprit.

Here is a simple example that can be used to reliably reproduce this issue:
VBox {
  nodeHPos: HPos.CENTER
  content: [
    ProgressBar {
      progress: Float.NaN
      onMouseClicked: function(e) {println("progress bar working")}
    }
    Button {
      text: "Click Me"
      onMouseClicked: function(e) {println("button working")}
    }
  ]
}

Upon running, both the ProgressBar and Button are inoperable. Mouse clicks, rollovers, and keystrokes are all disabled.